Year	number
2005	16.629032258064516
2006	16.595238095238095
2007	16.61904761904762
2008	16.246031746031747
2009	16.19685039370079
2010	16.181102362204726
2011	15.960629921259843
2012	16.023255813953487
2013	16.073576642335766
2014	16.133913043478262
2015	16.066642335766424
2016	16.052773722627734
2017	15.960291970802919
2018	15.672627737226275
2019	15.43992700729927